1. Field of the Invention
The present invention relates to a liquid ejection head and a liquid ejection apparatus, and more particularly to a structure of a liquid ejection head which is composed by joining together a plurality of head units.
2. Description of the Related Art
An inkjet head which is applied in an inkjet recording apparatus may adopt a mode in which a plurality of head units (head modules) are joined together. An inkjet head of this kind can print onto a wider printing region in one operation. Furthermore, in cases where the inkjet head does not pass manufacturing inspection, or where the inkjet head is replaced due to the occurrence of a fault or the end of the lifespan, then a further merit is obtained in that the head units can be replaced individually.
On the other hand, accurate positioning is required when joining together the head units. If variation occurs in the positions of the respective head units, then density non-uniformities (banding) occur in the joint sections between the head units.
In order to diminish density non-uniformities caused by discontinuity in the nozzle arrangement in the joint sections between head units of this kind, the head units (nozzles) are overlapped in the joint sections, so that the nozzle density in the joint sections is higher than the portions other than the joint sections, and the nozzles arranged at high density are selected appropriately to eject droplets, thereby diminishing the density non-uniformities in the image.
Japanese Patent Application Publication No. 2002-225255 discloses an inkjet recording apparatus including a head unit based on a mode in which a plurality of inkjet heads are joined together. The head units (nozzle row groups) are arranged in a staggered matrix fashion so as to be partially overlapping, and the production yield of the head units is increased by appropriately replacing defective inkjet heads.
Japanese Patent Application Publication No. 2007-261021 discloses an inkjet head unit in which a plurality of inkjet heads are arranged. The plurality of inkjet heads are arranged so as to be mutually overlapping in the lengthwise direction and in such a manner that the regions of the nozzles in the end portions of each inkjet head are not proximate to each other in the lengthwise direction.
Japanese Patent Application Publication No. 2009-66566 discloses a method of assembling a liquid ejection head in which a functional liquid ejection head is positioned at a prescribed position on a carriage, an adhesive is caused to flow in between the functional liquid ejection head and the carriage, and the functional liquid ejection head is maintained in a positioned state on the carriage, until the adhesive is solidified.
Japanese Patent Application Publication No. 2008-185365 discloses a head unit in which twelve inkjet heads are mounted on a sub carriage. The inkjet head is screw fastened to a head holding member and the head holding member is welded to a main body plate.
However, if the nozzle density is high in the joint sections between the head units, then this means that a nozzle in only one of one head unit or another head unit is used in order to form one dot. In this case, unused nozzles (redundant nozzles) arise in the joint sections.
Although it is possible to reduce the redundant nozzles by raising the positioning accuracy of the head units, it is difficult to raise the positioning accuracy of the head units when the installation (replacement) of the respective head units is taken into account.
Japanese Patent Application Publication Nos. 2002-225255, 2007-261021, 2009-66566 and 2008-185365 do not make any disclosure with respect to redundant nozzles in the joint sections between head units (inkjet heads). In other words, Japanese Patent Application Publication Nos. 2002-225255, 2007-261021, 2009-66566 and 2008-185365 do not refer to the technical problem of the present invention, or the method of solving this problem, namely, to reduce redundant nozzles in joint sections while making the positioning accuracy required between head units less strict.